1. Field of Invention
The present invention relates to relatively light weight offshore support structures and installation methods, specifically in which a vertical pipe column extending from the ground below to above the surface of the water is braced by a support assembly structure.
The preferred embodiment of the present invention includes a, support brace assembly configured to communicate with a vertical pipe column, said support brace assembly comprising two main inclined and radially spaced tubular legs, the upper ends of which, approximately five feet (5') to ten feet (10') below the water surface, are rigidly connected to a segment of a vertical pipe sleeve designed to be placed around the top of the pipe column, and the lower ends of which are rigidly connected to separate pile sleeves at the mud-line. Further, to provide an intermediate brace point to the pipe column, two inclined and radially spaced tubular braces extend from a hinged collar clamp around the vertical pipe column at their upper ends, located at approximately mid-height between the mud-line and the water surface, to rigid connections with the main tubular legs at the mud-line. Further, a vertical tubular member is located parallel to the pipe column, and rigidly connects to the pipe sleeve and main tubular legs at its upper end, and to the hinged collar clamp and tubular braces at its lower end. Secondary rigid tubular horizontals, diagonal braces, and a horizontal member at the mud-line, between the base of the main tubular legs and pile sleeves, complete the support brace assembly framing.
2. Prior Art & General Background
A list of prior patents which may be of interest is presented below:
______________________________________ U.S. Pat. No. Patentee(s) Issue Date ______________________________________ 2,637,978 J. R. Evans et al May 12, 1953 2,653,451 S. E. McCullough Sept. 29, 1953 2,927,435 M. M. Upson Sept. 23, 1956 3,306,052 Masasuke Kawasaki Feb. 28, 1967 3,372,745 B. G. Holmes March 12, 1968 3,390,531 L. P. Johnson et al July 2, 1968 3,516,259 A. J. Tokola June 23, 1970 3,524,322 I. C. Pogonowski Aug. 18, 1970 3,546,885 I. C. Pogonowski Dec. 15, 1970 3,556,210 Vincent C. Johnson Jan. 19, 1971 3,572,044 I. C. Pogonowski Mar. 23, 1971 3,638,436 Pogonowski Feb. 1, 1972 3,641,774 Hekkanen et al Feb. 15, 1972 3,716,994 Pogonowski Feb. 20, 1973 3,839,872 Loire Oct. 8, 1974 3,852,969 Gibson et al Dec. 10, 1974 3,876,181 Lucas Apr. 8, 1975 3,946,568 Heien Mar. 30, 1976 4,000,624 Chow Jan. 4, 1977 4,018,057 Erzen et al Apr. 19, 1977 4,036,426 Hansen Dec. 20, 1977 4,106,302 Vogel Aug. 15, 1978 4,109,476 Gracia Aug. 29, 1978 4,170,431 Wood Oct. 9, 1979 4,181,452 Pagezy et al Jan. 1, 1980 4,297,964 Oleborg Nov. 3, 1981 4,553,878 Willemse et al Nov. 19, 1985 4,557,629 Meek et al Dec. 10, 1985 4,558,973 Blandford Dec. 17, 1985 4,607,983 Meek et al Aug. 26, 1986 4,609,046 Schawann Sep. 2, 1986 4,616,708 da Mota Oct. 14, 1986 4,646,841 Schawann et al Mar. 3, 1987 4,669,917 Sveen Jun. 2, 1987 4,679,964 Blandford Jul. 14, 1987 4,687,380 Meek et al Aug. 18, 1987 4,688,967 Einstabland et al Aug. 25, 1987 4,702,321 Horton Oct. 27, 1987 4,740,107 Casbarian et al Apr. 26, 1988 4,761,097 Turner Aug. 2, 1988 4,812,080 Urquhart et al Mar. 14, 1989 4,818,145 Carruba Apr. 4, 1989 4,842,446 Carruba Jun. 27, 1989 4,854,778 Valenzuela Aug. 8, 1989 4,907,657 Cox Mar. 13, 1990 RE 30,823 Guy et al Dec. 15, 1981 RE 30,825 Guy et al Dec. 15, 1981 ______________________________________
The following publication is also referenced:
"Minimal platforms booming in shallow U.S. gulf waters", Jeff Littleton, Offshore (Incorporation THE OILMAN), November, 1988 (PennWell Publications 1988), Pages 22-28, 26 and figures. PA1 (a) the vertical pipe column is installed in the body of water by driving, or by other means, into the bottom soil; PA1 (b) with the vertical pipe column temporarily free-standing (bracing to a drilling rig or other installation equipment may be utilized), the prefabricated brace assembly is brought to the offshore site, and the brace assembly, with pre-loaded boat landing and piling and friction clamps as desired, is lifted off the transportation barge by the drilling rig; PA1 (c) the brace assembly is then lowered into the water, where upon it floats due to the buoyancy of closed tubular members, and the brace assembly is re-rigged for subsequent uprighting and installation on the pipe column (rigging may be pre-installed); PA1 (d) particular tubular members in the brace assembly are allowed to fill with water, causing the bottom end of the assembly to sink, and the entire brace assembly to self-upright; the hinged collar clamp at mid-height is brought loosely against the pipe column, the upper vertical pipe sleeve is lowered over the top of the pipe column, and then the hinged collar clamp is closed at mid-height, using divers; PA1 (e) the brace assembly is lowered further until its mudmat rests on the bottom soil, and the top end may be temporarily connected to the top of the vertical pipe column; PA1 (f) the two support piling are next driven or otherwise installed into the bottom soil, and connected to the pile sleeves with bolted friction pile clamps on tops of the pile sleeves, and/or with grout between the piles and the inside of the sleeves; PA1 (g) the connection from the vertical pipe column to the pipe sleeve, above water, is now welded with a conventional shim type connection; and the space between the pipe column and the inside of the pipe sleeve may also be filled with grout; and the erection of any supported platform, etc., may now proceed; and PA1 (h) the boat landing is permanently installed, and any temporary support pile guides or other installation aids are removed; platform installation is completed.
The prior art, both as disclosed in U.S. patents and in industry practice, has pursued reduced cost means of supporting single or multiple (e.g. 2 to 4) well production structures in the offshore environment in relatively shallow (e.g. 50' to 250') water depths. Reduced costs of placing wells into production may make possible the economic production of marginal wells and fields, heretofore considered uneconomical.
A well conductor pipe and well casings and tubings are usually installed by a jack-up type drilling rig in water depths up to two hundred and fifty (250') feet. The drilling rig is required for both drilling the well and for completing and preparing the well for production. Well conductor pipes are usually sized in the range of twenty-four (24") to forty-eight (48") inches in diameter, but are not capable of safely free-standing in over thirty (30',) to fifty (50') feet of water for any extended period of time, much less support a deck, helideck, etc., required for production of the well(s). In a typical installation, a relatively large and heavy support structure and platform are installed by a derrick barge after initial exploratory well drilling, and then subsequent re-mobilization of a drilling rig is required to complete the well(s).
Alternatively, a number of light support structure systems have been proposed to reduce time, cost, and to enhance the possibility that the jack-up drilling rig can be used for the complete structure installation. Several prior art methods make use of a single vertical pipe column as a principal support member, typically also used as a well conductor pipe. Such alternative type structures have been proposed and utilized, but most require extensive underwater diver installation work, or have been relatively flexible and produced objectionable movement, or have been very difficult or impossible to install with a jack-up drilling rig in water depths in the range of a hundred to two hundred and fifty feet (100'-250').
U.S. Pat. No. 4,558,973 is one such support structure, but has decided disadvantages. It requires four (4) or more pilings around the base of the structure, none of which are pre-installed in the structure. The structure is either split so as to clamp around the well conductor pipe, requiring extensive underwater installation work, or must be lifted completely out of the water for installation over the top of the conductor. The structure has extensive base mud-line framing, and is difficult or impossible to install with a conventional jack-up drilling rig in water depths over a hundred and twenty (125') feet.
U.S. Pat. No. 4,679,964 offers additional details and alternate embodiments of the above patent, as a continuation-in-part. Alternate means of connecting support piles, boat landings and decks, and mud-line framing members are presented. Alternate embodiments describe stacked structure sections, dual well caisson systems, and various cable stayed structures.
U.S. Pat. No. 4,687,380 discloses a structure comprised of a central column with three diagonal support legs and base connected piling. The three support legs are sleeve connected to the column to provide both lateral and vertical support. This structure system requires extensive underwater installation work, with dependency only on grouted column and pile connections. Piling are not pre-installed, and installation is difficult or impossible with a drilling rig in greater than a hundred and twenty to a hundred and fifty foot (125'-150') water depth.
U.S. Pat. No. 4,740,107 describes a structural system whereby two prefabricated sleeve and bracing assemblies, one above the water surface incorporating a boat landing, and one at the mud-line, are connected to a well caisson. Two or more vertical piling are driven into the bottom soil through sleeves in both assemblies, and connected to these sleeves to form a straight legged structure. This system is limited to approximately one hundred and twenty-five (125') feet or less water depth.
U.S. Pat. No. 4,818,145 discloses two (2) different types of support structures, both utilizing a well conductor pipe as one of three (3) supports at the mud-line. Two (2) pilings are added to form a three legged structure, and in this latter aspect has some similarity to the present invention. However, both structure types of the '145 patent have disadvantages. The first structure requires that the two added piling and structure legs extend to above the water surface, and requires difficult clamping to the well conductor pipe below water. Friction-type bolted clamps of tubular joints to underwater pipes have proven to give poor structural performance as well as installation difficulty. This structure is also relatively heavy, and difficult or impossible to install with a conventional drilling rig in water depths over seventy-five (75') to a hundred (100') feet.
The second of these support structures utilizes two (2) separate tubular braces hinges (pivotally) connected above the water to the well conductor pipe, and a hinge (pivotally) connected at the mud-line to two (2) separate piling. These types of hinge connections have proven to cause high structural flexibility, maintenance problems, and difficulty in installation. This system is limited in application for drilling rig installation to less than one hundred and twenty-five (125') to a hundred and fifty (150') foot water depths, and does not permit pre-loading of the piling.
U.S. Pat. No. 4,842,446 is a continuation-in-part of the preceding patent, and provides further details on both systems previously described. Alternate bracing configurations are described, with the purpose of reducing the amount of mud-line framing and diver work during installation. Both structure types continue to be limited in water depth application with drilling rig installation, as well as requiring difficult hinged or bolted connections.
A recent improvement to the above patents, presented in the industry by the same inventor, utilizes a totally submerged, two legged support structure, with two pilings connected at the mudline. The design, however, continues to have the disadvantages of difficult installation of bolted underwater clamps, extensive mud-line framing, inability to pre-load the piling, and very difficult or impossible drilling rig installation in the hundred and fifty (150') to two hundred and fifty (250') foot water depth range.
U.S. Pat. No. 4,812,080 discloses a structure with a vertical column braced by two inclined piles pre-loaded in a brace and sleeve assembly. This system requires difficult underwater connections, has piles which extend permanently above the water-line, and is difficult for drilling rig installation. Water depth range is limited to a maximum of a hundred (100') to a hundred and twenty-five (125') feet.
U.S. Pat. No. 4,854,778 discloses a structural system wherein a central tubular column is braced near its base by three vertical piles, braced by a template assembly to that column. This system is limited in water depth to approximately one hundred and twenty-five to one hundred and fifty (125-150') feet, and would be difficult to install with a drilling rig after a well is drilled.
U.S. Pat. No. 4,907,657 teaches of a structure very similar to that of U.S. Pat. No. 4,740,107 described above, but eliminates the lower (mud-line) prefabricated sleeve and bracing assembly. The structure is limited to much shallower water depths, in the range of fifty (50') to seventy-five (75') maximum depth.
A breasting dolphin type support structure, recently employed for relatively small offshore platforms, utilizes two inclined pilings connected to the well conductor pipe above the water-line using pile sleeves integrated with a boat landing structure. This unpatented system is limited to a maximum of a hundred foot (100') water depth, and is difficult for a drilling rig installation.
Submerged tripod and four-legged structures have also been utilized in the industry. These structures have not used the well conductor pipe as a principal support member, and are difficult or impossible to install by a drilling rig in any but relatively shallow (less than 100') water depths.
Relative the OILMAN reference, note in particular the "MOSS I" and "MOSS II" references as exemplified in the illustrations on page 26 of the article, wherein two alternated designs illustrate a minimal platform support structure not shown in the other prior art, but nonetheless readily distinguishable in design and implementation when compared to the present invention. Besides the structural differences associated with the present invention, the MOSS designs are configured to be installed in a manner wholly inconsistent in comparison with the present method.
Thus, in contrast to the present invention, there have been no offshore support structures which can be installed simply and inexpensively in up to two hundred and fifty foot (250') water depths with a conventional drilling rig, with a minimum of underwater installation work, and with the ability to pre-load support piling.